I found a lightly used one with the extended mag tube for @$250.
Essentially, it looks like a model 500, except it has the factory extended mag tube that goes to the end of the barrel. Is it basically a 500?
Is it a good gun? Basically equal to the 500, or is it cheaper made that should make me worry?
Will the Knoxx recoil stock from my regular 500 work on this gun?
Is 250 a reasonable price?

I have really been wanting a Rem 870 (tactical/police, or whatever you call it), but the price and possibility of switching the stock makes it an interesting possibility of a deal.
I would really appreciate some opinion, and especially knowledge of the interchangability.